Only one that really comes to mind is a double battle in Victory Road where the opponents had 2 Slaking along with a Gardevoir and Dusclops that spammed Skill Swap nonstop, really didn't help that my Swampert and Slaking were already very low on PP for their best moves (Surf and Hyper Beam respectively.) by the time I took out their Gardevoir and first Slaking and Dusclop's Pressure ability made that even worse for me until I took a risk and KO'd the Dusclops with a Faint Attack from Slaking to just barely survive a Brick Break from the enemy Slaking, Swampert seized victory for me with a critical Surf on the opposing Slaking right after Dusclops bit the dust.

But besides from that particular battle in Victory Road I'd have to say Tate & Liza just for constant Earthquake spamming.